1. Field of the Invention
The field of competitive protein binding assays or specific binding assays has greatly expanded, as its importance in the diagnostic field has become recognized. The ability to be able to detect a specific compound and measure the compound quantitatively has permitted the monitoring of the administration of a wide variety of drugs, the determination of an imbalance in a wide variety of hormones, the quantitation of physiologicaly active proteins, and the diagnosis of the presence of a pathogen. The different techniques have been distinguished in requiring or not requiring separation steps, the nature of the signal developed by a label, the development of the signal in a solution or on a surface and the manner of measurement for a quantitative determination.
In developing an assay, there are a number of considerations in devising the reagents and protocol. One consideration is the degree of sophistication of the individual performing the assay. There are many situations where it is desirable to have a relatively untrained individual to be able to carry out an assay and obtain reasonably quantitative results. In these situations, it is desirable that the assay be reasonably free from interference by materials in the sample, be relatively free of fluctuations with changes in environmental conditions and provide for easy measurement. Also, washings can be a source of error, either because of inadequate washing, leaving non-specific binding material, or by reversing specific binding.
2. Description of the Prior Art
U.S. Pat. No. 4,168,146 describes an immunoassay employing immunochromatography with antigens followed by contacting the immunochromatograph with an aqueous solution containing labeled antibodies. U.S. Pat. No. 4,233,402 describes a homogeneous assay method employing a combination of enzymes, where the substrate of one enzyme is the product of another. Enhanced production of the product is related to the amount of analyte in the assay medium. U.S. Pat. No. 4,275,149 describes the use of particles where combinations of enzymes may be employed, where the presence of the particles enhances the interaction between two enzymes, where the product of one enzyme is the substrate of the other. Enhanced production of the final product due to the presence of the two enzymes bound to the particle as a result of binding of specific binding pair members is related to the amount of analyte in the assay medium.